The goal of the proposed work is to develop a new technology: x-ray detectors based upon silicon drift detectors (SDD) specifically designed for optimal performance in the 500 eV to 10 keV region that will provide orders of magnitude advancement in energy dispersive x-ray detectors for biomedical research at Synchrotron Radiation (SR) research facilities. The proposed SDD detectors will be capable of attaining electronic noise below 10 e rms at peaking times as fast as 90 ns and will allow throughput rates of over 10 6 cps, and will not require cryogenic cooling. The projected increases in coat rate capability will allow x-ray absorption spectroscopy (XAS) research at ultra-low dilutions (or as a function of time, temperature, or concentration) that would otherwise be unfeasible or even impossible and enhance the capability of obtaining the direct structural,, bonding and compositional information which has been found to be so important in unraveling the mechanisms of protein and enzyme function at the molecular level. Successful completion of the phase I objectives and the initial results exceeding our Phase I goals show the feasibility of the approach in terms of low noise, high efficiency, and high count rate for x-rays. In Phase 2 we propose to develop the finalized SDD structures based upon the Phase 1 studies. In the first year we will continue development of the SDD structure and the integrated input transistor- preamplifier required to achieve the desired low noise and high rates, and development of the specialized housing for the integrated detector/FET. The signal processing electronics will utilize commercially available digital spectroscopy-signal pulse processors to obtain optimal performance from SDD detectors. In the second year we will construct and integrate nine elements of the detector system and deploy the array at the Stanford Synchrotron Radiation Laboratory (SSRL). PROPOSED COMMERCIAL APPLICATION: In Phase 3, we will develop commercial single and multiple detector systems based upon the Phase 1 & 2 efforts. These new detectors will lead to lower cost detector systems because:a)Single detectors using this new technology will attain count rates previously only possible with multi- element detectors, and b) Low cost of silicon planar processing. With significant improvements over existing detectors they could revolutionize the x-ray detector industry, replacing existing cryogenic detectors, and find new uses in x-ray instrumentation.